type
  TMyGrid = class(TDBGrid);

var
  Cell: TGridCoord;

procedure TForm1.DBGrid1DrawColumnCell(Sender: TObject; const Rect: TRect;
  DataCol: Integer; Column: TColumn; State: TGridDrawState);
begin
  if Cell.Y = TMyGrid(Sender).DataLink.ActiveRecord + 1 then
  begin
    dbgrid1.Canvas.Brush.Color := clLime;
  end;

  DBGrid1.DefaultDrawColumnCell(Rect, DataCol, Column, State);
end;

procedure TForm1.DBGrid1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
var
  vCell, OldCell: TGridCoord;
begin
  OldCell := Cell;
  Cell := TMyGrid(Sender).MouseCoord(X, Y);

  if OldCell.Y <> Cell.Y then
  begin
    TMyGrid(Sender).InvalidateRow(OldCell.Y);
    TMyGrid(Sender).InvalidateRow(Cell.Y);
  end;
end;